// tutorial01.c
// Code based on a tutorial by Martin Bohme (boehme@inb.uni-luebeckREMOVETHIS.de)
// and another tutorial by Stephen Dranger (dranger at gmail dot com)
// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1

// A small sample program that shows how to use libavformat and libavcodec to
// read video from a file.
//
// Use
//
// gcc -o tutorial01 tutorial01.c -lavformat -lavcodec -lswscale -lz
//
// to build (assuming libavformat and libavcodec and libswscale are correctly installed
// your system).
//
// Run using
//
// tutorial01 myvideofile.mpg
//
// to write the first five frames from "myvideofile.mpg" to disk in PPM
// format.

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>

#include <stdio.h>

void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
	FILE *pFile;
	char szFilename[32];
	int y;

	// Open file
	sprintf(szFilename, "frame%d.ppm", iFrame);
	pFile = fopen(szFilename, "wb");
	if (pFile == NULL)
		return;

	// Write header
	fprintf(pFile, "P6\n%d %d\n255\n", width, height);

	// Write pixel data
	for (y = 0; y < height; y++)
		fwrite(pFrame->data[0] + y * pFrame->linesize[0], 1, width * 3, pFile);

	// Close file
	fclose(pFile);
}

int main(int argc, char *argv[]) {
	AVFormatContext *pFormatCtx = NULL;
	int i, videoStream;
	AVCodecContext *pCodecCtx;
	AVCodec *pCodec;
	AVFrame *pFrame;
	AVFrame *pFrameRGB;
	struct SwsContext * pSwsCtx;
	AVPacket packet;
	int frameFinished;
	int numBytes;
	uint8_t *buffer;

	if (argc < 2) {
		printf("Please provide a movie file\n");
		return -1;
	}
	// Register all formats and codecs
	av_register_all();

	// Open video file
	if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0)
		return -1; // Couldn't open file

	// Retrieve stream information
	if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
		return -1; // Couldn't find stream information

	// Dump information about file onto standard error
	av_dump_format(pFormatCtx, 0, argv[1], 0);

	// Find the first video stream
	videoStream = -1;
	for (i = 0; i < pFormatCtx->nb_streams; i++)
		if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
			videoStream = i;
			break;
		}
	if (videoStream == -1)
		return -1; // Didn't find a video stream

	// Get a pointer to the codec context for the video stream
	pCodecCtx = pFormatCtx->streams[videoStream]->codec;

	// Find the decoder for the video stream
	pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
	if (pCodec == NULL) {
		fprintf(stderr, "Unsupported codec!\n");
		return -1; // Codec not found
	}
	// Open codec
	if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
		return -1; // Could not open codec

	// Allocate video frame
	pFrame = avcodec_alloc_frame();

	// Allocate an AVFrame structure
	pFrameRGB = avcodec_alloc_frame();
	if (pFrameRGB == NULL)
		return -1;

	// Determine required buffer size and allocate buffer
	numBytes = avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
			pCodecCtx->height);
	buffer = (uint8_t *) av_malloc(numBytes * sizeof(uint8_t));

	// Assign appropriate parts of buffer to image planes in pFrameRGB
	// Note that pFrameRGB is an AVFrame, but AVFrame is a superset
	// of AVPicture
	avpicture_fill((AVPicture *) pFrameRGB, buffer, PIX_FMT_RGB24,
			pCodecCtx->width, pCodecCtx->height);

	pSwsCtx = sws_getContext(pCodecCtx->width,
			pCodecCtx->height, pCodecCtx->pix_fmt,
			pCodecCtx->width, pCodecCtx->height,
			PIX_FMT_RGB24, SWS_FAST_BILINEAR, NULL, NULL, NULL);

	if (pSwsCtx == NULL) {
		fprintf(stderr, "Cannot initialize the sws context\n");
		return -1;
	}

	// Read frames and save first five frames to disk
	i = 0;
	while (av_read_frame(pFormatCtx, &packet) >= 0) {
		// Is this a packet from the video stream?
		if (packet.stream_index == videoStream) {
			// Decode video frame
			avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

			// Did we get a video frame?
			if (frameFinished) {

				// Convert the image from its native format to RGB
				sws_scale(pSwsCtx,
							(const uint8_t * const *) pFrame->data,
							pFrame->linesize, 0, pCodecCtx->height,
							pFrameRGB->data,
							pFrameRGB->linesize);

				// Save the frame to disk
				if (++i <= 5)
					SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height,
							i);
			}
		}

		// Free the packet that was allocated by av_read_frame
		av_free_packet(&packet);
	}

	// Free the RGB image
	av_free(buffer);
	av_free(pFrameRGB);

	// Free the YUV frame
	av_free(pFrame);

	// Close the codec
	avcodec_close(pCodecCtx);

	// Close the video file
	avformat_close_input(&pFormatCtx);

	return 0;
}
